1. Field of the Invention
This invention relates to a novel sulfur-containing (thio)ether (co)polymer and an optical element therewith. The sulfur-containing (thio)ether (co)polymer of this invention is a thermoplastic optical resin with excellent optical, mechanical and thermal properties, which can be prepared in a good productivity and is useful for optical elements such as an optical disk substrate; a liquid-crystal plastic substrate; various optical lenses including an eye-glass; and an LED sealing coat.
2. Description of the Prior Art
An essential property is transparency for an optical material. To date, various industrial resins with good transparency are known; for example, polymethyl methacrylate(PMMA), bisphenol-A-polycarbonate (Bis-A-PC), polystyrene (PS), methyl methacrylate-styrene copolymer (MS), styrene-acrylonitrile copolymer (SAN), poly(4-methylpentene-1) (TPX), polycycloolefin (COP), poly(diethyleneglycol bisallylcarbonate) (EGAC) and polythiourethane (PTU).
PMMA exhibits good transparency, weather resistance and moldability, but has drawbacks such as a lower refractive index (n.sub.d) of 1.49 and a higher water absorbency.
Bis-A-PC exhibits good transparency, heat resistance and impact resistance and a higher refractive index, but also exhibits a larger chromatic aberration, which limits its application.
PS and MS exhibit good moldability and transparency as well as a lower water absorbency and a higher refractive index, but exhibit lower impact resistance, weather resistance and heat resistance. They have been, therefore, rarely used as an optical resin in practice.
SAN is believed to have a relatively higher refractive index and well-balanced mechanical properties, but it is inadequately heat resistant (heat-distortion temperature: 80 to 90.degree. C.) to be used as an optical resin.
TPX and COP exhibit good transparency, lower water absorbency and good heat resistance, but have drawbacks such as a lower refractive index (n.sub.d =1.47 to 1.53), lower impact resistance and lower gas barrier property.
EGAC is a thermosetting resin from diethyleneglycol bisallylcarbonate monomer, which is most frequently used for a general-purpose eyeglass. It exhibits good transparency, good heat resistance and a minimal chromatic aberration, but has drawbacks such as a lower refractive index (n.sub.d =1.50) and lower impact resistance.
PTU is a thermosetting resin prepared by reaction of a diisocyanate with a polythiol, which is most frequently used for a superhigh refractive index eyeglass. It is an excellent material with good transparency, good impact resistance, a higher refractive index and a lower chromatic aberration, but has only one drawback of a longer duration for thermal-polymerization molding (1 to 3 days); i.e., there is a problem in productivity.
As described above, optical resins of the prior art have good properties, but they have their specific problems to be solved. Thus, it has been earnestly desired to develop a thermoplastic optical resin with good optical, mechanical and thermal properties as well as a good productivity and a higher refractive index.